System and method for sensing white paper

ABSTRACT

Apparatus and methods are provided for sensing the presence of bright white paper on a conveyor of a paper sorting system. The conveyor is constantly illuminated with ultraviolet light. When bright white paper is present in the inspection zone of the conveyor, it will re-radiate fluorescent light energy as a result of the ultraviolet light. Periodically, the inspection zone of the conveyor is illuminated with a second light source in the visible light spectrum. Light is collected from the inspection zone of the conveyor, including reflected light from the secondary source and including emitted fluorescent light energy as a result of the ultraviolet light falling on bright white paper. Periodically a microprocessor associated with the sensor senses reflected light from the second source to determine whether any object if present on the conveyor. The microprocessor then senses the level of fluorescent light energy being emitted from any object on the conveyor. The system determines first whether any object is present on the conveyor, as a result of the reflected secondary light, and then determines whether that object is bright white paper depending upon the measured level of emitted fluorescent light energy. Based upon these determinations, the stream of waste paper on the conveyor can be sorted into two fractions, one of which is the bright white paper.

APPLICATION FOR UNITED STATES LETTERS PATENT

[0001] Be it known that I, Russell S. Bruner, a citizen of the UnitedStates residing at 726 Poplar Avenue, Mt. Juliet, Tenn. 37122 and I,David R. Morgan, a citizen of the United States residing at 9921 U.S.Highway 68 East, Benton, Ky. 42025, and I, Garry R. Kenny, a citizen ofthe United States residing at 6299 McDaniel Rd., College Grove, Tenn.37046, have invented a new and useful “System and Method For SensingWhite Paper.”

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a system and method for sortingmass recyclables and more particularly to a system for sensing andsorting white paper from other objects.

[0003] It will be appreciated by those skilled in the art that societydesires to recycle as much of its waste materials as possible. Forexample, aluminum cans, plastic bottles, and other items have been thesource of mixed recyclable efforts in the past. The assignee of thepresent application, Magnetic Separation Systems, Inc. (MSS) is a worldleader in mixed recyclables. MSS is also the owner of many patentsdisclosing technologies for sorting and concentrating aluminum andsorting plastics.

[0004] One other type of mixed recyclable is paper. In the past,recyclable efforts have been dominated by hand sorting of paper by type.One common effort is curbside recycling. Other efforts have been to sortpaper from other types of materials. Unfortunately, as with any otherprocedure, any type of hand sorting requires an intensive use of laborthat is not always efficient.

[0005] What is needed, then, is a method and system that can sort whitepaper from a stream of other paper. This needed system must also becapable of sorting a stream of material from white paper in case thestream is dominated by materials other than white paper. The system mustdecrease the amount of labor presently being used. The system must beeconomical. The system must be effective. The system is presentlylacking in prior art.

SUMMARY OF THE INVENTION

[0006] The present invention discloses a system and method for sortingwhite paper, and especially a type of white paper commonly referred toas bright white paper, from other objects. One reason that recycling ofbright white paper is very desirable is that the fluorescent chemicalsadded to such papers are expensive plus the bright white paper tends tobe a very high quality paper fiber. Thus, this is a premium paperfraction for recycling. The system may also sort other objects fromwhite paper.

[0007] The present invention uses an energy source that is preferably anultraviolet light light that is concentrated in some manner onto anobject. The energy is focused on the paper. If the paper is bright whitepaper, the ultraviolet radiation will cause the brightening agents inthe white paper to fluorescence into an energy having a different andlonger wavelength. The fluorescence is then measured.

[0008] The system and method of the present invention is particularlyadapted for use in sensing the presence of bright white paper that flowspast the sensor on a conveyor. The conveyor is constantly illuminatedwith the ultraviolet light. Also, a second light source is providedwhich periodically illuminates an inspection zone of the conveyor with asecond light which is in the visible light spectrum, and preferably inthe blue-green portion of the visible light spectrum.

[0009] A sensor located above the inspection zone of the conveyorcollects light from the inspection zone of the conveyor. The collectedlight includes both emitted fluorescence from bright white paper locatedin the inspection zone and reflected light from the second light sourcereflected off of objects in the inspection zone.

[0010] Periodically, the sensing system senses first and secondparameters of the light collected from the inspection zone. The firstparameter is the level of reflection of the second light source in orderto determine whether any object is present on the conveyor in theinspection zone. The second parameter sensed is the level of fluorescentlight to determine whether an object present in the inspection zone isbright white paper.

[0011] Thus, if the sensed level of the reflected light from the secondlight source is below a certain threshold, the system will determinethat no object is present in the inspection zone on the conveyor. If thesensed level of reflected light from the second light source is above athreshold level, the system will sense that some object is present inthe inspection zone on the conveyor, but the identification of thatobject will depend upon the sensed level of fluorescent energy comingfrom that object. If the sensed level of fluorescent energy from theobject is below a threshold level, the system will determine that theobject is something other than bright white paper. If the sensed levelof fluorescent energy is above a predetermined threshold, the systemwill determine that the sensed object is bright white paper.

[0012] The system may then send control signals to an ejection meanswhich will eject either the bright white paper fraction or thenon-bright white paper fraction from the paper stream flowing across theconveyor.

[0013] Accordingly one object of the present invention is to provide asystem and method for sensing and sorting bright white paper from otherobjects.

[0014] Another object of the present invention is to provide a systemthat allows someone to sort bright white paper from other objects thatis not labor intensive.

[0015] Another object of the present invention is to provide a systemthat can sort both bright white paper from other objects and otherobjects from bright white paper.

[0016] Still a further object of the present invention is to provide anaccurate system for sensing bright white paper.

[0017] Other and further objects features and advantages of the presentinvention will be readily apparent to those skilled in the art upon areading of the following disclosure when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a block diagram of the system and method of the presentinvention.

[0019]FIG. 2 is an optical diagram of the system and method of thepresent invention.

[0020]FIG. 3 is a block diagram of the secondary light source of thepresent invention.

[0021]FIG. 4 is an elevation view of one half of the reflector of thepresent invention as viewed from the side of the conveyor.

[0022]FIG. 5a is a plan view of a lens of a sensor element.

[0023]FIG. 5b is an elevation view of the lens of FIG. 5a.

[0024]FIG. 5c is a schematic elevation partly sectioned view of asensing element showing the lens in place within a collimator tubewhich, in turn, is in place within a lens housing.

[0025]FIG. 6a is a bottom view of a sensor housing, showing the layoutof an array of lens cavities and cavities for receiving the second lightsources.

[0026]FIG. 6b is an elevation sectioned view of the sensor housing,taken along line 6 b-6 b of FIG. 6a. FIG. 6b shows the cavity in whichthe lens is received.

[0027]FIG. 6c is another elevation sectioned view through the sensorhousing, taken along line 6 c-6 c of FIG. 6a. FIG. 6c illustratescavities in which the second light source elements are placed.

[0028]FIG. 7 is an elevation view of the sensor of the present inventionas viewed from the side of the conveyor.

[0029]FIG. 8 is a schematic plan view of the conveyor showing theinspection zone.

[0030]FIG. 9 is a schematic side elevation view of the sensor in placeabove a conveyor, and also shows an associated ejection system forejecting a fraction of the flowing paper stream in response to signalsfrom the sensor.

[0031]FIG. 10 is a graph illustrating the wavelength of the ultravioletenergy source and of the emitted fluorescent energy from bright whitepaper. Also shown is a high frequency cut-off of a filter.

[0032]FIG. 11 is a block diagram of the electrical control system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Referring now the drawings, and particularly to FIG. 1, thesystem of the present invention is shown and generally designated by thenumeral 10. The system 10 includes a first light source 12 whichpreferably is an ultraviolet light source 12. Ultraviolet light energyemitted from source 12 travels along paths 13 to a concentrator means 14which then directs the light along paths 15 so as to focus theultraviolet light energy on an inspection zone or focal zone 19 on aconveyor 100 located below the apparatus 10. A portion of any lightenergy reflected from or emitted from any objects within the inspectionzone 19 will travel upward as indicated by path 17 to a sensor 16. If anobject such as 102 is located in the inspection zone 19, the lightreflected from and/or emitted from the object 102 in inspection zone 109and received by sensor 16 can be examined to determine the nature of theobject 102, and particularly to determine whether the object 102 isbright white paper. Other objects 101, 104 and 106 are alsoschematically illustrated in place upon the conveyor belt 100.

[0034] The system 10 is particularly designed to determine whether anobject in the inspection zone 19 is bright white paper. Bright whitepaper is a common name for a type of high quality paper commonly used inoffices for printers and copiers. Bright white paper is typically a highquality paper fiber which has been treated with brighteners which causethe paper to fluoresce in the presence of ultraviolet light. Whenultraviolet light energy falls upon bright white paper, the brightenersin the object will fluoresce and will emit light energy having awavelength in the range of from about 400 to about 550 nanometers, whichis in the visible light spectrum. The fluorescent energy emitted frombright white paper when an ultraviolet light is shown on it is greatwhen compared to the amount of fluorescent energy that will be emittedfrom objects other than bright white paper.

[0035]FIG. 3 schematically illustrates a second feature of the system 10which includes a second light source 20. As will be further describedbelow, the second light source 20 is contained within a common housingwith the sensor 16. The second light source 20 is preferably a source ofvisible light energy. One preferred second light source 20 is a bluelight emitting diode which emits light energy having a wavelength ofapproximately 480 nanometers. Light from the second light source 20travels downward along path 21 and is reflected off an object such asobject 102 located within the inspection zone 19. The reflected lightenergy travels back upward along path 23 where it is also received bythe sensor 16.

[0036] As will be further described below, the general purpose of thesecond light source 20 is to provide a means for detecting whether anyobject is present on the conveyor belt 100 within the inspection zone19. The sensor 16 and its associated control apparatus will becalibrated so that when the reflected light 23 exceeds a certainthreshold, it will provide a determination that some object other thanthe black conveyor belt 100 is located within the inspection zone 19. Asecond determination will then be made as to the level of fluorescentenergy traveling upward along path 17 to the sensor 16. If an object ispresent in the inspection zone 19, but the level of fluorescent energyis below a predetermined threshold, the system 10 will determine thatthe object is not the desired bright white paper. On the other hand, ifan object is determined to be present, and the amount of fluorescentenergy 17 emitted by that object is above the predetermined threshold,the system 10 will determine that the object is bright white paper.

[0037]FIG. 10 is a graphical illustration of the electromagneticradiation energy which might be picked up by sensor 16. The horizontalaxis represents the wavelength of the electromagnetic radiation, and thevertical axis represents the relative intensity of radiation.

[0038] There is a peak at approximately 360 nanometers in FIG. 10 whichrepresents the frequency of the ultraviolet light energy radiating fromsource 12. To the extent that ultraviolet energy is merely reflected offof the focal zone 19 and received by sensor 16, it would create a spikeas shown in FIG. 10.

[0039] As previously noted, when ultraviolet light energy falls upon apiece of bright white paper containing fluorescing additives, theadditives fluoresce, thus converting some of the ultraviolet lightenergy into visible light energy having a longer wavelength (and thuslower frequency). In FIG. 10, a hump in the detected energy generallydesignated at 118 is representative of the fluorescent energy emittedfrom a piece of bright white paper. As is apparent in FIG. 10, the hump118 begins at a wavelength of approximately 400 nanometers, peaks atabout 440 nanometers, then drops off and is essentially absent at about550 nanometers wavelength.

[0040] In order to isolate the fluorescent energy emitted from brightwhite paper, the sensor 16 preferably has a filtering means associatedtherewith. Preferably the filtering means is a band pass filter whichwill allow light energy only within the range of from 400 to 500nanometers length to pass therethrough. The details of construction ofthis filtering means are further described below. In FIG. 10, the highfrequency, and thus short wavelength, cut off of the filter is indicatedby the curve 120. Since this high frequency cut off is at a lowerfrequency than the ultraviolet light source, reflected ultraviolet lightenergy will not be sensed by sensor 16.

[0041] The secondary light source 20 previously described operates at awavelength of 480 nanometers, so that when the secondary light sourcereflects off of an object within the inspection zone 19 that reflectedlight 23 can pass through the filter means.

[0042]FIG. 7 is an elevation sectioned view of the sensing system 10 inplace over the conveyor 100.

[0043] The first light source 12 is a light module 46 which includesfour parallel elongated tubular ultraviolet light bulbs 48 which areseen in cross-section in FIG. 7. The light bulbs 48 extend transversallyacross the width of the conveyor 100 perpendicular to the direction ofpaper flow indicated by the arrow 110. The bulbs 48 are contained withina housing 52. Electronic starters 50 are associated with the bulbs 48and cause the same to turn on and off when electrical power is directedthereto in a well known manner. A glass panel 54 covers the lower sideof module 46.

[0044] Thus, most of the ultraviolet light energy from bulbs 48 isemitted laterally as along the paths 13 previously noted, where it fallsupon the concentrators 14. The concentrators 14 are preferably curvedreflectors formed in the shape of an arc of an ellipse so that all lightfalling thereon will be reflected toward a focal point 58 lying in thecenter of the inspection zone 19 on the conveyor 100. The ultravioletlight energy reflected from concentrators 14 follows paths generallydesignated as 15 to the focal point 58.

[0045] The geometric layout of the concentrator 14 is best illustratedin the schematic representation shown in FIG. 2. As indicated in FIG. 2,the light source 12 has a central point 112 which is generallycoincident with the upper focal point 112 of an ellipse 114 upon whichthe reflecting walls of concentrator 14 lie. The lower focal point 58 ofthe ellipse 114 falls upon the conveyor 100 in the center of theinspection zone 19.

[0046] Referring now to FIGS. 4 and 7, the concentrator 14 isconstructed from first and second reflecting walls 24 and 25 which aresupported within a housing 60 of the apparatus 10 by a plurality ofbrackets such as 26 and 27. The reflector walls 24 and 25 are preferablypolished stainless steel. The brackets such as bracket 26 shown in FIG.4 may also be manufactured from stainless steel.

[0047] The lower end of the housing 60 of apparatus 10 is closed by atransparent glass shield 116 which allows the light energy to passtherethrough while preventing dirt, paper and debris from entering theapparatus 10.

[0048] The reflecting walls 24 and 25 may be generally described as anelliptical reflecting lens having focal point 58 within the inspectionzone 19.

[0049] Referring now to FIGS. 6a, 6 b and 6 c, a sensor housing or lenshousing is shown and generally designated by the numeral 124. The sensorhousing 124 is an elongated housing which lies across the width of theconveyor 100 and can be described as being transverse to and isperpendicular to the direction of travel 110 along the conveyor belt100.

[0050] The sensor housing 124 has a plurality of lens cavities 42 and aplurality of secondary light source cavities 126 defined therein. Anarray of sensor elements are carried by housing 124.

[0051]FIG. 6b is a sectioned view taken along lines 6 b-6 b of FIG. 6a,showing the details of construction of one of the lens cavities 42.

[0052]FIG. 6c is a sectioned view taken along lines 6 c-6 c of FIG. 6a,showing the details of construction of two secondary light sourcecavities 126.

[0053] The sensor housing is held in place by a bracket 56 as shown inFIG. 7.

[0054] Turning now to FIGS. 5a-5 c, the details of construction of oneof the sensing elements of sensor 16 will be described.

[0055]FIG. 5c is a schematic elevation cross-section view similar toFIG. 6b and schematically illustrating the components of one sensingelement 128 of sensor 16. Each sensing element such as 128 is associatedwith one of the lens cavities 42.

[0056] A collimator tube 40 is received in each lens cavity 42 and heldin place therein by set screws received through threaded holes 130 (SeeFIG. 6b). In one preferred embodiment each collimator tube isapproximately 4″ long, 1″ outside diameter and ¾″ inside diameter. Thecollimator tube 40 may be an aluminum tube having a matte black finish.The collimator tube 40 ensures that the light being collected by thesensing element 128 is substantially only light traveling directlyupward from an object immediately below sensing element 128 in the focalzone 19.

[0057] Located at the upper end of each collimator tube 40 is asemi-spherical lens 32. Plan and side elevation views of one lens 32 areshown in FIGS. 5a and 5 b, respectively.

[0058] Located immediately above the lens 32 is the filtering means 122which includes first and second optical filter plates 34 and 36. Thefirst optical filter plate is a high frequency pass filter 34, and thesecond optical filter plate 36 is a low frequency pass plate 36. As willbe understood by those skilled in the art, the filter plates 34 and 36can be selected to determine the frequencies of light energy whichreally will not pass therethrough. Filter plates 34 and 36 are standardoptical filters which are available from Edmund Scientific.

[0059] The light energy which passes through the lens 32 is focusedwithin a cone having outer boundaries along the dashed arrows 132 and134 which focuses that energy upon a photo electric detector 38. Thephoto electric detector 38 is a silicone photo diode.

[0060] Thus, the band pass filter means 122 will pass fluorescent energyhaving a wavelength longer than a lower limit of about 400 nanometers,which lower limit is longer than the wavelength of the ultraviolet lightfrom source 12. The filtering means 122 will further block fluorescentenergy having a wavelength longer than an upper limit, which in theillustrated embodiment is preferably about 500 nanometers. The range oflight energy having wavelength from 400 to 500 nanometers can bedescribed as being in the blue-green portion of the visible lightspectrum.

[0061] As previously noted, the light emitted from second light source20 has a wavelength of approximately 480 nanometers, which will bepassed by the filtering means 122 when said light is reflected from anobject in the inspection zone 19.

[0062] Referring now to FIG. 9, a general layout of the system 10 andassociated conveyor apparatus is shown, whereby the sensor system 10 maybe utilized to detect bright white paper on the conveyor 100 and to sendcontrol signals to an ejector mechanism 70 which uses air jets 80 toeject paper from the conveyor 100.

[0063] The conveyor 100, ejector system 70 and associated apparatus areshown in detail in an application of Michael R. Grubbs et al., entitledPAPER SORTING SYSTEM, U.S. patent application Ser. No.______, filedsimultaneously herewith, and assigned to the assignee of the presentinvention. The details of construction of the system shown in the Grubbset al. application are incorporated herein by reference as if the samewere fully set forth herein.

[0064]FIG. 8 is a schematic plan view of the conveyor 100 illustratingan elongated strip shaped inspection zone 19 lying across a width 142 ofthe conveyor belt 100. The focal point 58 previously described withregard to the side elevation view of the ellipse is in fact a focal line58 which defines the center line of the inspection zone 19.

[0065] In the system shown in FIG. 9 the first conveyor 100 conveys thepaper objects 102 from right to left so that they pass under the sensor16. The conveyor 100 is traveling at a very great rate of speed (as muchas 1200 ft/min), and as the objects reach the left hand end of conveyor100 they are launched off of the conveyor 100 and fly through the airacross an ejection gap 136 toward a product conveyor 138.

[0066] Signals from the photo electric detector 38 are converted intodigital signals which are directed to a microprocessor 140 whichperforms the measuring, sensing, comparing and evaluating functions. Themicroprocessor 140 will go through the evaluation steps described below,and at appropriate times will send a control signal to the ejectorsystem 70 to direct compressed air to jet 80 so that the air jet 80 willbe directed against an object which at that time is passing across theejection gap 136. Any object impacted by an air jet as it crosses thegap 136 will be blown downward between the two conveyors 100 and 138 andwill be part of an ejected paper stream fraction. Non-ejected paper willflow across the gap 136 and fall onto the conveyor 138 which will takeit to another location.

[0067]FIG. 11 is a schematic block diagram of the control system of theapparatus 10.

[0068] The microprocessor 140 may be a XYCOM model PCD1048microprocessor available from XYCOM Automation, Inc. The microprocessor140 preferably has touch screen operated control station 144 whichallows system variables to be changed and the sort selection to bechanged. The system provides the ability to perform a positive sortwhere non-bright white paper is ejected or a reverse sort where thebright white paper is ejected when the concentration of the targetedpaper is less than that of the non-targeted paper.

[0069] The microprocessor 140 is connected by interface 146 to powersupply ballasts 148 and then to the ultraviolet light source 12.

[0070] The microprocessor 140 is connected by a ribbon cable 150 to arear receiver board 152 which is in turn connected by a ribbon cable 154to the sensor unit 16 and the secondary light sources 20 contained inthe sensor housing.

[0071] A power supply 156 is connected to the rear receiver board 152.

[0072] An LED power supply 158 is connected to the secondary lightsource 20.

[0073] The rear receiver board 152 includes amplifiers and analog todigital converters. Signals from the sensor 16 are communicated overcable 154 to the rear receiver board 152 where they are amplified anddigitized before being passed over cable 150 to the microprocessor 140.

[0074] The microprocessor 140 also communicates over cable 160 to theejector control system 70 which includes a plurality of solenoid driverboards 162 and an array of solenoid valves 164 which control the flow ofair to the air jets 80. A solenoid power supply 166 is connected to thedriver boards 162.

METHODS OF OPERATION

[0075] The methods of operation of the present invention will now bedescribed with reference to FIGS. 7 and 9.

[0076] The system 10 provides an apparatus and method for sensing thepresence of bright white paper on the conveyor 100 of the paper sortingsystem like that described in the Grubbs et al. application which hasbeen incorporated herein by reference.

[0077] The conveyor 100 is directing a stream of waste paper from rightto left as seen in FIG. 8 at a very high speed below the sensor 16.

[0078] The ultraviolet light source 12 is constantly on and constantlyilluminates the inspection zone 19 on the conveyor belt 100 immediatelybelow the sensor 16. As previously described, that ultraviolet lightenergy is focused on the inspection zone 19 by means of the ellipticalshaped walls 24 and 25.

[0079] When a piece of paper such as 102 passes through the inspectionzone 19, if the paper 102 is bright white paper, it will fluoresce andwill re-radiate fluorescent light energy from the bright white paper. Aspreviously described with reference to FIG. 1, a portion of thatfluorescent energy will travel directly upward along the path 17 to thesensor 16.

[0080] Throughout this process, the inspection zone 19 will also beperiodically illuminated with light from the second light source 20,which as previously noted is preferably a blue light emitting diode. Ina preferred embodiment, the secondary light source 20 illuminates theinspection zone 19 every 3 milliseconds.

[0081] Light from the inspection zone 19, including both reflected lightand emitted fluorescent light, is collected by the collimator tube 40and passes through the lens 32 and the filtering means 122 to the photoelectric detector 38. The photo electric detector 38 will convert thelight energy into an electrical signal, which, in turn, is convertedinto a digital electric signal which is directed to the microprocessor140.

[0082] A first measuring step or sensing step is performed bymicroprocessor 12 when the secondary light source 20 is on. This firstsensed parameter will thus indicate the level of reflected light fromsecondary source 20, and if that level of reflected secondary lightexceeds a predetermined threshold, the microprocessor 140 will determinethat some object is present in the inspection zone 19 on the conveyor100. Then, when the secondary light source 20 is off, the microprocessor140 will perform a second measuring or sensing step while only theultraviolet light illuminates the inspection zone 19. In this secondstep, the sensed light energy will be compared to the predeterminedthreshold for fluorescent energy, and if that threshold is exceeded, themicroprocessor 140 will determine that an object present in theinspection zone 19 is bright white paper.

[0083] The microprocessor 140 can be described as periodically sensingfirst and second parameters of the light collected by the sensingelement. The first parameter is the level of reflection from theinspection zone 19 of light originating with the secondary light source20. If this first parameter exceeds a certain threshold, an indicationis generated indicating that some object is present in the inspectionzone 19 other than the conveyor belt 100 itself.

[0084] The second parameter sensed by the microprocessor 14 is the levelof fluorescent light energy which has been radiated from an objectwithin the inspection zone 19. If this level of fluorescent light energyexceeds a predetermined threshold, this will generate an indication thatan object which is present in the inspection zone 19 is, in fact, brightwhite paper.

[0085] If the first parameter indicates that an object is present, butthe second parameter indicates that the object is not bright whitepaper, then it is known that the object is one which should be separatedfrom the bright white paper.

[0086] Depending upon the signals generated by the microprocessor 140, acontrol signal is then sent to the ejection system 70 to directcompressed air to air jets 80 to eject a selected fraction of the streamof paper which is moving along the conveyor 100. It will be appreciatedthat the microprocessor 140 can be programmed to either eject the brightwhite paper or to eject the non-bright white paper. Preferably,whichever type of paper comprises the smaller portion of the stream ofpaper flowing across conveyor 100 will be ejected, whereas the majorportion will be allowed to flow across to the product conveyor 138.

[0087] The periodic illumination by secondary source 100 is preferablyperformed approximately every 3 milliseconds. In general, it may bedescribed as being performed in excess of 100 times per second.Preferably the microprocessor 140 periodically senses the light beingcollected from the inspection zone 19 at the same periodic rate at whichthe secondary light source 20 is illuminating the inspection zone 19.

[0088] The paper objects will be traveling on the conveyor 100 at aspeed of approximately 1200 feet per minute or 20 feet per second, thusby strobing every 3 milliseconds, a piece of letter size paper, 8½″ widewould be strobed at least 10 times as it passed under the sensor 16.

[0089] The sensor 16 and associated microprocessor 140 can be describedas an evaluating means for evaluating the level of fluorescent energydetected by each of the sensing elements to determine whether brightwhite paper is located below each sensing element.

[0090] As previously noted, there is preferably a linear array ofsensing elements arranged across the width of the conveyor belt. Forexample, for a 48″ wide conveyor, there may be 32 sensor elements.Signals from each of the sensing elements are separately analyzed, andcontrol signals are separately sent to an array of 32 air jets 80, sothat there is an ejection air jet 80 associated with each of the sensingelements. Thus, a paper object may be located toward one edge of theconveyor belt and its location will be determined by the identificationof the sensing elements which sense the presence of that objecttherebelow. Then the associated air jets can be activated at the propertime to blow the sensed object through the ejection gap 136 if desired.

[0091] Thus, it is seen that the apparatus and methods of the presentinvention readily achieve the ends and advantages mentioned, as well asthose inherent therein. While certain preferred embodiments of theinvention have been illustrated and described for purposes of thepresent disclosure, numerous changes in the arrangement and constructionof parts and steps may be made by those skilled in the art, whichchanges are encompassed within the scope and spirit of the presentinvention as defined by the appended claims.

What is claimed is:
 1. A method for determining whether an object iswhite paper comprising the steps of: a) transmitting ultraviolet lightonto said object; b) receiving fluorescent energy created by saidobject; and c) measuring said fluorescent energy.
 2. The method of claim1 further comprising the step of filtering said fluorescent energy. 3.The method of claim 2 wherein said filtering step includes passingfluorescent energy having a wavelength longer than a lower limit, saidlower limit being longer than a wavelength of said ultraviolet light. 4.The method of claim 3, wherein said lower limit is about 400 nanometers.5. The method of claim 3, wherein said filtering step includes blockingfluorescent energy having a wavelength higher than an upper limit. 6.The method of claim 3, further comprising the steps of: a) transmittinga second light onto said object, the second light having a wavelengththat will be passed by said filtering step; and b) measuring said secondlight reflected from said object.
 7. The method of claim 1 furthercomprising the steps of: a) transmitting a second light onto saidobject; and b) measuring said second light reflected from said object.8. A method for determining whether an object is white paper comprisingthe steps of: a) transmitting light onto said object; b) receivingfluorescent energy from said object; and c) measuring said fluorescentenergy.
 9. The method of claim 8 further comprising the step offiltering said fluorescent energy.
 10. A system for determining whetheran object is white paper comprising: a) a first light source; b) asensor for measuring fluorescent energy created by said object as aresult of said object receiving light energy from said first lightsource.
 11. The system of claim 10 further comprising a filter locatedbetween said object and said sensor for passing to said sensorfluorescent energy having a wavelength above a lower limit.
 12. Thesystem of claim 11 wherein said first light source is ultraviolet. 13.The system of claim 12 further comprising: a) a second light source; andb) wherein the sensor is constructed to measure light from said secondlight source reflected from said object at a wavelength outside theultraviolet spectrum.
 14. The system of claim 13, wherein fluorescentenergy passed by said filter is within the visible light spectrum. 15.The system of claim 13 wherein said second light source is at awavelength in the visible light spectrum.
 16. The system of claim 11wherein said filter is a band pass filter.
 17. The system of claim 11,wherein said filter comprises a low pass element and a high passelement.
 18. The system of claim 11 wherein said filter passeswavelengths of substantially between 400 and 500 nanometers.
 19. Amethod of sensing the presence of bright white paper on a conveyor of apaper sorting system, the method comprising the steps of: a) constantlyilluminating an inspection zone of the conveyor with ultraviolet light;b) when bright white paper is present in the inspection zone,re-radiating fluorescent light from the bright white paper; c)periodically illuminating the inspection zone of the conveyor with asecond light having a longer wavelength than the ultraviolet light; d)collecting light from the inspection zone of the conveyor; e)periodically sensing first and second parameters of the light collectedin step (d), the first parameter being the level of reflection of thesecond light in order to determine whether any object is present in theinspection zone, and the second parameter being the level of fluorescentlight to determine whether an object present in the inspection zone isbright white paper.
 20. The method of claim 19, further comprising:controlling an ejection system of the paper sorting system to eject aselected fraction of a stream of paper objects moving along theconveyor, in response to the determination in step (e) of whether theobjects are bright white paper.
 21. The method of claim 19, wherein: a)step (a) includes providing the ultraviolet light from an elongatedultraviolet light source oriented across a width of the conveyortransverse to a direction of flow of objects on the conveyor; and b) themethod further includes a step of focusing the ultraviolet light uponthe inspection zone of the conveyor, the inspection zone being a stripacross the width of the conveyor.
 22. The method of claim 19, wherein:step (d) includes collecting the light through an array of collimatortubes.
 23. The method of claim 19, further comprising: filtering thelight collected in step (d) to only pass a predetermined bandwidth oflight wavelengths to a sensor.
 24. The method of claim 23, wherein thepredetermined bandwidth is in the blue-green portion of the visiblelight spectrum.
 25. The method of claim 19, wherein step (c) and thesensing of the first parameter in step (e) are performed at the sameperiodic rate.
 26. The method of claim 25, wherein the periodic rate isin excess of one hundred events per second.
 27. A sensor apparatus forsensing the presence of white paper traveling past the sensor apparatuson a conveyor, comprising: a) an ultraviolet light source; b) an arrayof sensing elements located above the conveyor; and c) evaluation meansfor evaluating the level of fluorescent energy detected by each of thesensing elements to determine whether white paper is located below eachsensing element.
 28. The apparatus of claim 27, further comprising: areflector arranged to reflect ultraviolet light from the source onto afocal zone of the conveyor.
 29. The apparatus of claim 28, furthercomprising: an array of collimator tubes, each one of the tubes beingassociated with a respective one of the sensing elements, the collimatortubes being located above the focal zone, so that fluorescent energyfrom white paper in the focal zone passes through the collimator tubesto the sensing elements.
 30. The apparatus of claim 28, wherein: a) theultraviolet light source is located above the array of sensor elements;and b) the reflector is a two-sided reflector which is located to thesides away from the sensor elements to reflect light originating abovethe sensor elements to the focal zone located below the sensor elements.31. A sensor apparatus for sensing the presence of an object on aconveyor comprising: a) an energy source located above the conveyor andextending transversely to a length of the conveyor; b) a reflectorpositioned relative to the energy source and the conveyor so as toreflect energy from the energy source onto an elongated strip shapedinspection zone extending across a width of the conveyor; and c) asensor located above the inspection zone.
 32. The apparatus of claim 31,wherein: the reflector includes two reflecting walls on opposite sidesof the energy source.
 33. The apparatus of claim 32, wherein thereflecting walls are shaped as arcs of an ellipse.
 34. The apparatus ofclaim 31, wherein the reflector includes an elliptical reflecting lenshaving a focal point within the inspection zone.
 35. The apparatus ofclaim 31, wherein: the energy source includes at least one elongatedtubular light source extending across the width of the conveyor.
 36. Theapparatus of claim 31, wherein: the sensor includes a linear array ofsensing elements located above and parallel to the inspection zone forreceiving energy travelling upward from the inspection zone.